Ajax boss Erik ten Hag blamed a computer error after January signing Sebastien Haller was mistakenly left out of the club's Europa League squad.

Haller, 26, was not included on the list of players submitted to Uefa before Tuesday's deadline.

"It is of course incredibly annoying," said Ten Hag.

"Haller was indeed on the list, but it is an administrative error. Something went wrong with the computers, just a check mark on and off."

The Ivorian striker has already scored twice in six appearances for Ajax since joining from West Ham last month for more than £20m.

However, as it stands he will be ineligible when the 34-time Dutch champions take on French side Lille in the Europa League last 32 later this month.

Ten Hag says he takes responsibility for the mistake and will do everything he can to try and rectify it.

"In the first instance, [technical director] Marc Overmars and I are responsible," he added. "Of course, people makes mistakes, but this is a top sports organisation. This mistake should never have happened.

"Haller is of course also very disappointed. Although he also understands that this was not done on purpose..

"But we will keep trying as long as there is hope."

Arsenal included new midfield loan signing Martin Odegaard in their squad, along with goalkeeper Mat Ryan, on loan from Brighton.

Manchester United, who have dropped into the Europa League, added 18-year-old winger Amad Diallo to their list. The teenager recently signed from Atalanta.